214 CHEMICAL ENGINEERING
The instrument is of .rather wider utility than is claimed by the manufacturers, even such material as copper drillings being shredded up by it, though in such cases the cups and cones furnished by the makers might profitably be replaced by those of chrome or manganese steel. For certain materials I have also found better results were obtained by running the cone in the opposite direction from that indicated by the manufacturer.
Symons Disc Crusher.—The range of this machine, shown in Fig. 10, is in the larger sizes, crushing from 6 in. to IK in. It is claimed that the largest sizes will crush to an inch but all factors considered the higher figure would be the practical minimum size which it will deliver. The two discs A and B, are held in place by
FIG. 10.—Symons disc crusher,
two shafts one of which is hollow and contains the other. The large ball and socket termination of the inner shaft allows the inner shaft actuated by the eccentric E to partake of a rocking motion so there* is constantly changing set between the two discs and they are constantly changing the angle they make with one another. The inner shaft gyrates in a direction reverse to the rotation of the disc A. The material entering the feed spout is thrown out to the periphery of the two discs by centrifugal force. If a fragment is caught near an outlet point of the discs which happens momentarily to be a close together it will be released and thrown out by centrifugal force after the width of exit is increased under rotation. If a larger fragment is caught between the discs when they are at or nearly at their point of greatest set it will be carried around and crushed when the discs come closer together and will then be thrown out into the enclosing hopper. A magnetic tramp-iron separator is necessary ahead of a disc crusher. It is virtually a gyratory crusher turned on its side.
Disc grinders are also made in which the discs are parallel and pulverizing takes place through attrition between the faces, which may be either plane or grooved. After all, they are a variation of the old fashioned buhr-stone, set vertical instead of horizontal, and of steel or cast-iron instead of stone.
For the shredding of fibrous materials, paper, rags, etc., the beater of the paper makers may be employed. As may be seen from the illustration, this consists of a heavy wheel with bars set in (practically a roll with corrugations